BEIJING -- Beijing will shut down smoke-belching factories and ban thousands of cars from city streets to improve air quality during next year's Olympic Games, a senior city official said on Thursday.

Vice mayor Ji Lin said other special measures would include a ban on dust-causing earthworks at construction sites.

Ji said 120 billion yuan ($15.69 billion) had already been invested in environmental improvements over the past decade and at least another 25 billion yuan would be spent over the next year to clean the city's air.

"Beijing attaches high importance to environmental protection and much investment and progress has been made," he told a news conference.

"But problems still exist and there is a long way to go to meet the higher standards needed for the Olympic Games. We are confident we will achieve our goals."

Improving air quality is one of the biggest issues facing Beijing. Despite improvements in the past few years, the city is still regularly blanketed in smog.

Some polluting factories have been given time limits to reduce emissions and others will have restricted operations from Aug. 8 to 24 next year.

"During the Games we will have stricter measures," Ji said. "Some companies will adjust their production time, some will have to reduce production and some will be suspended."

Just how many of the city's three million cars will be kept off the streets had yet to be decided, Ji said.

"We also have to consider what impact these measures will have on people's lives," he said.

CLOGGING DUST

Tens of thousands of coal-fired boilers, ovens and furnaces have been converted to use natural gas, while 50,000 old taxis and 10,000 buses will be taken off the roads by next August.

Action has been taken to ensure that the city's many construction sites do not add to the choking dust in the air, while cement factories and brickyards have also been shut down.

The Beijing Coking and Chemical Works has been permanently closed and the city's worst polluter, the Shougang steel works, has closed a blast furnace and a coke oven as it begins its relocation to a new site outside the city.

Ji said there would be no need for Olympic delegations to bring their own experts and equipment to measure air quality in Beijing during the Games.

"At Olympic venues and villages, we will set up mobile air quality stations and the information from those will be provided to anyone who wants it," he said.